Duktape VS jerryscript

Fast math optimizations can break code like this by breaking isNaN.

I was porting a C++ project to a certain platform - and that platform enabled a -ffast-math equivalent by default in Release (but not Debug) builds! This broke duktape, a JS engine said project embedded, in some nasty and subtle ways. Instead of storing a number/pointer/??? (8 bytes) + type tag (4? bytes) for each dynamically typed JS value, duktape can bit-pack values into a single 8 byte "double" value by storing object/string handles as NaN values - this isn't an uncommon trick for dynamically typed scripting stuff:

https://github.com/svaarala/duktape/blob/c3722054ea4a4e50f48...

Naturally, the -ffast-math equivalent broke isNaN checks, which caused random object/string handles to be mistakenly reinterpreted as "numbers" - but only in Release builds, for this one particular platform, in one rarely taken branch, so neither QA nor CI caught it, leading to hours of manufacturing a repro case, stepping through an absurd amount of code, and then finally looking at the default build rules and facepalming.

Cursing the platform vendor under my breath, I overrode the defaults to align with the defaults of every other config x platform combination we already had: no fast math. If you want those optimizations, use SSE-friendly NaN-avoiding intrinsics - or, if you must use the compiler flags, ensure you do so consistently across build configs and platforms, perhaps limited to a few TUs or modules if possible. This allows you to have a chance at using your Debug builds to debug the resulting "optimizations".

Sure. For example, DukTape is an implementation of Javascript designed to be embedded in other projects. Google's V8 Javascript engine (used in Chrome), can also be embedded, see Node.Js for example.

- Duktape (4.8k stars)

Based on JerryScript, the creators also provide an IDE and serial communication tool on their website. There's also ample documentation and guides. Looking forward to getting more into this.

I hear you loud and clear.

There are subsets of JS for embedded device e.g. Espruino https://github.com/espruino/Espruino for BangleJS https://shop.espruino.com/banglejs also with 4MB or JerryScript https://jerryscript.net

Fitbit uses Jerryscript in some of their watch OSes. Well, at least they were last time I was tinkering with making my own watch face

https://jerryscript.net/

- JerryScript (5.8k stars)

jerryscript-project / jerryscript

Nice comparison of js engines can be found in the issues here https://github.com/jerryscript-project/jerryscript/issues/43...